Google is removing the legacy Google Search Console messages on August 1, 2022. If you try to access the old messages console Google has a warning at the top that reads "Important: This report won't be available after Aug 1, 2022. Please use the new Message panel instead."
Here is a screenshot (click to enlarge):
This should come as no surprise, in February, Google moved more of the legacy messages to the new message panel. There Google "finished the migration of all the messages into the new Search Console interface." So why would you need the old legacy message viewer?
Just note, the new message panel rolled out in 2019, so it took a few years to get here.
This was spotted by Maximilian Wenzel on Twitter.
Forum discussion at Twitter.
